Microwave antenna

ABSTRACT

A MICROWAVE ANTENNA OF THE ARRAY ANTENNA TYPE IS PROVIDED WITH A TRANSMISSION LINE NETWORK COMPRISING TWO SUPPLY LINES FOR PRODUCING A CORRESPONDING NUMBER OF BEAMS. THE ANTENNA IS FORMED BY VARIOUS PARALLEL LINEAR ARRAYS. A SEPARATE FREQUENCY BAND IS ALLOCATED TO EACH OF THE SUPPLY LINES. THE SUPPLY LINES ARE CONNECTED TO ALL LINEAR ARRAYS BY MEANS OF FREQUENCY-SELECTIVE COUPLERS (E.G. DIPLEXERS), EACH SO DESIGNED THAT THEY FEED THE COMBINED SIGNALS OF VARIOUS FREQUENCY BANDS TO BE TRANSMITTED TO THE ASSOCIATED LINEAR ARRAYS, WHILE THEY FEED THE RECEIVED SIGNALS SEPARATED ACCORDING TO FREQUENCY BAND TO THE VARIOUS SUPPLY LINES.

Feb. 27, 1973 H. T. HUELE MICROWAVE ANTENNA 3 Sheets-Sheet 1 Filed Aug.11, 1971 INVENTOR HENDRIK TEUNIS HUELE AGENT H. T. HUELE Feb. 27, 1973MICROWAVE ANTENNA 5 Sheets-Sheet 2 Filed Aug. l l., 1.971

Feb. 27, 1973 H. T. HUELE 3,718,933

MICROWAVE ANTENNA Filed Aug. 11, 1971 3 Sheets-Sheet 3 United StatesPatent O ce lands Filed Aug. 11, 1971, Ser. No. 170,711 Int. Cl. H01q13/10 US. Cl. 343-768 3 Claims ABSTRACT OF THE DISCLOSURE A microwaveantenna of the array antenna type is provided with a transmission linenetwork comprising two supply lines for producing a corresponding numberof beams. The antenna is formed by various parallel linear arrays. Aseparate frequency band is allocated to each of the supply lines. Thesupply lines are connected to all linear arrays by means offrequency-selective couplers (e.g. diplexers), each so designed thatthey feed the combined signals of various frequency bands to betransmitted to the associated linear arrays, while they feed thereceived signals separated according to frequency band to the varioussupply lines.

The invention relates to a microwave antenna of the planar array type,comprising a number of radiating elements and a transmission linenetwork, which contains two supply lines, a number offrequency-selective coupling members and a number of directionalcouplers, each of the supply lines, suitable for producing microwaveenergy in an own frequency band, being connected to a number of commonfrequency-selective coupling members via a number of directionalcouplers, said coupling members combining the supplied microwave energyand transmitting this energy to the radiating elements in order toproduce a number of beams corresponding with the number of supply lines,whereas the incoming signals are separated by the coupling membersaccording to frequency band and supplied to the corresponding supplylines.

Such antennae are known, for example, from US. Pat. No. 3,518,689 issuedto I. A. Algeo et al. The antenna decribed by Algeo is employed toprovide two directionally frequency-scanned energy beams, the one beamscanning in elevation with little appreciable motion in azimuth and theother beam scanning in azimuth with little appreciable motion inelevation. Therefore, this antenna comprises a matrix array of radiatingelements, the rows of which are fed by a first frequency-scanned feedand the columns of which are fed by a second frequencyscanned feed,whereby two controlled cross-scanning bearns may be simultaneouslyproduced.

Such antennae, particularly the frequency-selective coupling membersbetween the feeds and the radiators are unsuited for simultaneouslyproducing two beams of different but neighbouring frequency bands; inthat case the supply lines afiect each other so that the antennaefficiency and the antenna gain are adversely affected. Such antennaefurther require many radiating elements and the construction of theemployed horn is difiicult to realize and very expensive.

The invention has for its object to construct a microwave antenna of thekind set forth for producing simultaneously two beams with highefficiency and maximum antenna gain.

According to the invention the radiating elements in such an antennaconsist of a number of slotted waveguides corresponding with the numberof frequency-selective coupling members, the slots having a bandwidthsuited for transmission of the microwave energy of two different butneighbouring frequency bands and each of the fre- Patented Feb. 27, 1973quency selective coupling members being constituted by a diplexer.

The invention and its advantages will be described more fully withreference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating the embodiment of the microwave antennaaccording to the invention;

FIG. 2 is a perspective view, partly cut away, of the embodiment of saidmicrowave antenna.

FIG. 3 is a perspective view of one arrangement of a coupler, whichconnects a supply line to a frequency-selective coupling member.

In FIGS. 1 and 2 reference numeral 1 designates a microwave antenna ofthe array type formed by slotted waveguides and connected to atransmission line network 2 having two supply lines 7 and 8. Each of thesupply lines 7, 8 has its own frequency band I and II respectively,

slightly differing from each other. The two supply lines are eachterminated at one end by a non-reflecting load 15 and 16 respectively.Said supply lines are connected to all linear arrays of the antennathrough a number of frequency-selective coupling members correspondingwith the number of parallel linear arrays. For the sake of simplicity itis assumed here that the planar array antenna comprises only fourparallel linear arrays 3, 4, 5 and 6 and, therefore, fourfrequency-selective coupling members 9, 10, 11 and 12. These members 9,10, 11 and 12 are each constructed so that they feed the signals ofdifferent frequency bands to be transmitted together to the associatedlinear arrays, whereas they supply the received signals separatedaccording to frequency band to the corresponding supply line.

Said parallel linear arrays 3, 4, 5 and 6 form one planar array antenna.Each of these linear arrays consists of a waveguide having slots 13 andclosed in a conventional manner at one end by a non-reflecting load 14,the other end forming the input or the output of the waveguide.

Since the antenna according to the invention uses signals in twofrequency bands, transmission line network 2 has to be provided withmeans for feeding the signals of said frequency bands together to alllinear arrays of the planar array antenna, and with means for separatingthe received echo signals according to frequency band. This is achievedin a particularly simple manner since both for joining and forseparating, one and the same frequency-selective coupler known from thefrequency-diversity technique, termed diplexer may be employed. Sincethe employed diplexers 9, 10, 11 and 12 are identical, it may sufiice todescribe only diplexer 9. It comprises two Waveguides 17 and 18, whichare coupled by two directional couplers 19 and 19' (so-called short slothybirds) arranged at a given distance from each other.

Each of the waveguides 17 and 18 comprises a filter 20 and 20, which maybe of any suitable type, provided that they pass signals from supplyline 8 in band H and stop signals from supply line 7 in band I. So thecharacteristics of the filters 20, 20- are determined in accordance withthe operational frequency of the two supply lines 7, 8 which have to becoupled to the linear array of radiators. The filters have a negligiblereactance for frequency band II and a very high reactance for frequencyband I and may be of any suitable type, e.g. a waveguide internallyprovided with one or more irrisses. Waveguide 18 is terminated at oneend by a non-reflecting load 21.

Apart from said supply lines 7 and 8 and diplexers 9, 10, 11 and 12 thetransmission line network 2 comprises four directional couplers 22, 23,24 and 25 associated with supply line 7 and four directional couplers22', 23', 24', and 25' associated with supply line '8. These directionalcouplers are coupled with the associated supply line at a given distancefrom each other.

FIG. 3 shows how directional coupler 22 is coupled with supply line 7.If it is assumed that a signal in frequency band II occurs at the inputof supply line 8, a directional coupler such as 22' feeds a givenquantity of signal energy from the supply line 8 to the diplexer 9 towhich said coupler 22' is connected.

The signal energy fed into waveguide 17 is divided into two equalquantities at the short slot hybrids 19; one quantity A is transmittedto the filter 20' and the other quantity B to filter 20 through hybrid19'. Said energy quantity A has a wave amplitude which is times as largeas the wave amplitude of the original signal energy, coupled intowaveguide 17 by directional coupler 22'. This energy quantity A is notshifted in phase. Energy quantity B transmitted through hybrid 19', hasalso a wave amplitude which is times as large as the wave amplitude ofthe the original energy, however, the phase of this energy quantity hasincreased by 90 degrees.

Both energy quantities A and B pass the filter part of the diplexer,after which each energy quantity A and B is split at hybrid 19. QuantityA is split into two equal portions A and A A is the energy portion whichis transmitted to the linear array 3 and has a Wave amplitude which istimes as large as the wave amplitude of energy portion A therefore, thisenergy portion A has a wave amplitude which is /2 times as large as thewave amplitude of said original energy; the phase of the energy portionA remains 90 degrees. After energy portion A has passed the hybrid 19 inthe direction of the directional coupler 22, the corresponding waveamplitude is also /2 times as large as the wave amplitude of saidoriginal energy. However, the phase shift is increased to 180 degrees.After energy quantity B passed the filter 19', said quantity B isdivided into two equal portions B and B at hybrid 19.

Energy portion B remaining in the same waveguide, has a wave amplitudewhich is /2 times as large as the wave amplitude of quantity B and so awave amplitude which is /2 times as large as the wave amplitude of theoriginal energy from supply line 8; the phase of this energy portion Bremains degree.

The energy portions A and B have the same wave amplitude, but thecorresponding waves are in phase opposition; therefore the waves of theenergy portions A and B are quenched and nothing of the original energyfrom supply line 8 can be transmitted to the other supply line 7. Afterthe energy portion B has passed hybrid 19, this energy portion has alsoa wave amplitude which is /2 times as large as the wave amplitude of theoriginal energy, while its phase-shift is increased to 90 degrees.Therefore, energy portions A and B have the same wave amplitude, each ofwhich is /2 times as large as the Wave amplitude of the original waveenergy; also the phase of waves A and B are the same. By superpositionof the two waves, it is obvious that the whole wave energy from supplyline 8 is transmitted to linear array 3.

An analogous argument applies to the wave energy fed from supply line 7to diplexer 9 by directional coupler 22. This microwave energy is firstsplit into two equal quantities C and D at hybrid 19, energy quantity Cbeing transmitted to filter 20 and energy quantity D to filter 20'.After reflection by the filters 20, 20' each of the quantities of energyC and D is divided into two equal portions C and C or D and Drespectively. Energy portions C and D are gathered in the part ofwaveguide 17, which is connected to supply line 7; these energy portionsC and D have the same amplitude, but the corresponding waves are inanti-phase; therefore, the waves of the energy portions C and D arequenched. However, energy portions C and D which are transmitted tolinear array 3 are identical in wave amplitude and phase; therefore thewhole energy fed from supply line 7 by directional coupler 22 istransmitted to linear array 3. Each of said diplexers joins the signalenergy of the two frequency bands I and II derived from the two supplylines and supplies the joined energy to one of the parallel lineararrays. Since the required frequencies for producing the cosecF-shapedbeam and the pencil-shaped beam do not differ much, one type of slotscan be used in the linear arrays. The bandwidth of the slots is suchthat both frequencies are passed.

Echoes from remote targets are received by the antenna and fed to therespective diplexers 9, 10, 11 and 12. These diplexers operate asfrequency splitters for the incoming signals so that the latter areseparated according to frequency band, the signals of frequency band Ibeing fed to supply line 7 through directional couplers 22, 23, 24 and25 and the signals of frequency band H being fed to supply,

line 8 through directional couplers 22', 23', 24' and 25.

The antenna described above permits of transmitting and receiving withinone and the same antenna aperture in two frequency bands I and II, thesignals of frequency band I being transmitted and received in a first,for example, cosec. -shaped beam and the signals of frequency band IIbeing transmitted and received in a second, for example, pencil-shapedbeam. The plane of the cosec. shaped pattern has to be perpendicular tothe planar array while the pattern of the pencil-shaped beam has to bepositioned in said plane of the coscF-shaped pattern. The cosec. -shapeof the first beam and the position of its plane is determined by theamplitude and phase ratio of the signals of frequency band I, when asuitable center frequency is used, as supplied to the respective lineararrays. Also the pencil-shape of the second beam and its position in theplane of the cosec. -beam are determined by the amplitude and phaseratio of the signals of frequency band II, which are fed to therespective linear arrays. The correct amplitude and phase ratio for eachof these beams is obtained by a correct choice of the coupling factor ofthe consecutive directional couplers and of each of the supply lines andby a correct choice of the length of the piece of supply line betweeneach pair of consecutive directional couplers. However, there is onlyone frequency for the pencil-shaped beam, whereas the amplitude andphase ratio is such that the beam is entirely in the plane of thecosec.'--shaped pattern. For other frequencies the pencil-shaped beam isnot exactly in said plane. Since the pencil-shaped beam should be keptas much as possible in the plane of the cosec. -shaped pattern, onlyslight variations in the frequency of band II are allowed. However, toobtain a beam for scanning in elevation, the amplitude and phase ratiohas to vary considerably. This is obtained when a rectangular waveguideshaped as a so-called serpentine is used as supply line 8, as shown inFIG. 2; consequently the physical distance between the consecutivedirectional couplers is considerably shorter than the length of thepiece of waveguide between said consecutive directional couplers. As isknown, it is possible, when using such a serpentine waveguide forfeeding a planar array antenna, to obtain a frequency-controlled beam.The direction of the beam then depends upon the frequency of the signalssupplied to the serpentine waveguide. This property may be utilized forcontrolling the pencil-shaped beam so that the latter can perform ascanning movement in the plane of the cosec. -shaped beam pattern. Itwill be obvious that this makes a three-dimensional target positionindication possible. The loops of the serpentine waveguide provide thedesired dispersion. If, however, the beam has to be independent of thefrequency, as is, for example, the case with the cosecF-shaped beam, itis necessary for the supply line 7 not to be dispersive.

Frequency-independent phase shifters such as 26 must then be provided tobring about the desired phase variation across the antenna aperture.Since the microwave antenna according to the invention uses supply lineseach having its own frequency band, these supply lines cannot influenceeach other so that a high antenna efficiency and a maximum antenna gaincan be obtained.

The microwave antenna according to the invention is not restricted tothe embodiment described above. For example, a fan-shaped beam patternmay be employed instead of a cosecP-shaped beam pattern.

What I claim is:

1. A microwave antenna of the planar array type, comprising a number ofradiating elements and a transmission line network, which contains twosupply lines, a number of frequency-selective coupling members and anumber of directional couplers, each of the supply lines, suitable forproducing microwave energy in its own frequency band, being connected toa number of common frequency-selective coupling members via a number ofdirectional couplers, said coupling members combining the suppliedmicrowave energy and transmitting this energy to the radiating elementsin order to produce a number of beams corresponding with the number ofsupply lines, whereas the incoming signals are separated by the couplingmembers according to frequency band and supplied to the correspondingsupply lines, wherein the radiating elements consist of a number ofslotted waveguides, corresponding with the number of frequency-selectivecoupling members, the slots having a bandwidth suited for transmissionof the microwave energy of two different but neighbouring frequencybands, and each of the frequency-selective coupling members beingconstituted by a diplexer.

2. A microwave antenna as claimed in claim 1, wherein the directionalcouplers are arranged at a given relative distance along the waveguidethe amplitude and phase ratio of the quantities of energy, coupled outfor the one supply line, being chosen so that the planar array antennahas a cosecP-shaped transmitting-receiving pattern, whereas for theother supply line the amplitude and phase ratio of the quantities ofenergy coupled out are chosen so that the planar array antenna has apencil-shaped transmitting-receiving pattern in the plane of the saidcosecP- shaped beam.

3. A microwave antenna as claimed in claim 2, wherein said other supplyline is formed by a rectangular waveguide shaped into a so-calledserpentine supply line so that the physical distance between consecutivedirectional couplers is considerably shorter than the length of thepiece of waveguide between said consecutive directional couplers,whilst, when the carrier frequency of the signal fed to said supply lineis varied within the frequency band allotted to said supply line, thepencil-shaped beam produced performs a scanning movement in the plane ofsaid cosec. -shaped beam.

References Cited UNITED STATES PATENTS 3,270,336 8/1966 Birge 3438543,434,139 3/1969 Algeo 343-854 3,518,689 6/1970 Algeo et a1 434854 JOHNS. HEYMAN, Primary Examiner US. Cl. X.R. 34377l, 854

